The present invention relates to an image processing apparatus as well as to an image processing method for processing image signals transmitted from an image pick-up tube or an image pick-up element, and more specifically to an image processing apparatus and an image processing method for suppressing flickers of a fluorescent lamp as well as to a computer-readable recording medium with a program for making a computer execute the method stored therein.
Generally a television camera (an image pick-up device) for picking up image of an object converts pixel information to an image signals for enabling reproduction of an image on a television receiver. In this step, the pixel information is expressed with brightness values for pixels two-dimensionally distributed, and the television camera (an image pick-up device) converts the pixel information to one-dimensional image signals based on a prespecified transmission system.
In a television system, generally luster scanning is employed as processing for conversion to one-dimensional image signals, namely as scanning, and basically image information for an entire screen is fetched by means of horizontal scanning for fetching a brightness value or color information at each pixel position on a screen and vertical scanning for repeatedly executing the horizontal scanning from a top to a bottom of a screen. Especially skip scanning is executed in which the horizontal scanning is executed for every nxe2x88x921 scanning lines and the vertical scanning is executed n times for the entire screen. To form a screen, namely one frame in the skip scanning, n times of vertical scanning, namely n fields are required.
As a transmission system for a color television currently being used, there are the three systems of NTSC system, PAL system, and SECAM system, but herein consideration is made for a case,where the NTSC system is employed.
In the NTSC system, the number of scanning lines is 525 lines, and one frame comprises two fields, one consisting of an odd number field and another consisting of an even number field. Also in the NTSC system, a frame frequency is 30 Hz, namely scanning is executed at a rate of 60 fields per second.
When picking up image of an object using an analog type of image pick-up tube as a television camera based on this NTSC system and a fluorescent lamp using a 50 Hz power as illumination, image signals each including twinkling with a constant cycle, namely flickers are generated. FIG. 7 is an explanatory view for illustrating field scanning in a television camera using a 50 Hz power fluorescent lamp and executing scanning at a rate of 60 fields per second and flickers generated under the conditions.
As shown in FIG. 7, in ordinary fluorescent lamps generally used outdoors, flickers with a frequency of 100 Hz, namely discharge of a {fraction (1/100)} second cycle is repeated with a 50 Hz AD voltage. In contrast, in a television camera executing scanning at a rate of 60 fields per second, {fraction (1/60)} second is required for scanning one field. For this reason, both a time required for executing discharge 5 times in a fluorescent lamp and a time required for 3 times of field scanning in a television camera executing scanning a rate of 60 fields per second are {fraction (1/20)} sec, and under this time interval, discharge timing in the fluorescent matches timing for scanning pixel positions within one field of the television camera.
Immediately after a discharge voltage is loaded to a fluorescent lamp, the brightness becomes relatively high, so that also a reflected light from an object at the point of time and on has relatively large magnitude, and a large signal can be obtained at a pixel position with a reflected light having large magnitude therefrom detected at the point of time. When this signal is transmitted as an image signal to a television receiver for reproduction of the image, twinkling with a frequency of 20 Hz, namely flickers is felt.
For instance, in FIG. 7, under the discharge timings No. 1, No. 6, and No.11 in a fluorescent lamp as well as the scanning times for fields No. 1, No. 4, and No. 7 in a television camera, flickers No. a1, No. a2, and No. a3 corresponding thereto respectively are generated. Also for other discharge numbers in the fluorescent lamp and other fields each having a different field number in a television camera, flickers for 3 fields numbered as b1, b2 and b3; c1, c2 and c3; d1, d2 and d3; or e1, e2 and e3 as one cycle respectively is generated.
Also in a case where a digital type of solid image pick-up device such as a CCD (Charge Coupled Device) is used as a television camera, as a shuttering speed of a shutter for making pixels arrayed two-dimensionally receive a reflected light from an object is equivalent to a field scanning frequency in an analog type of image pick-up tube, if the shuttering speed is 60 Hz or 60 times per second, the flickers described above is generated.
So there has been proposed an image pick-up device capable of suppressing flickers in a fluorescent lamp for suppressing the flickers as described above. FIG. 8 is a block diagram showing general configuration of an image pick-up device capable of suppressing flickers in a fluorescent lamp based on the conventional technology.
In. FIG. 8, a brightness signal outputted from an image pick-up element 101 is inputted into a gain control unit 102, and a level of the inputted brightness signal is adjusted therein. The brightness signal is transmitted via the gain control unit 102 to an A/D converter 103 to convert the signal to a digital signal, and the converted signal is subjected to appropriate signal processing in a digital image signal processing unit 104. The digital brightness signal having been subjected to digitalizing processing in the image signal processing unit 104 is transmitted to the D/A converter 105 and is converted to an analog signal therein, and is displayed as an image in an output device 106.
The digital brightness signal having been subjected to the digitalizing processing in the image signal processing unit 104 is also transmitted to an integrator 107. In the integrator 107, an integrated value digital data signal for one field is generated by adding thereto each of the digital brightness signals sequentially transmitted as described above. The generated integrated value digital data signal is transmitted to a gain computing unit 108. In the gain computing unit 108, a gain is computed by dividing a reference value by an integrated value indicated by the integrated value digital data signal.
Herein the integrated value digital data signal is a signal including an excessive brightness signal generated due to flickers, and by computing a gain with the gain computing unit 108, correction of an integrated value digital data signal not including a reference value, namely flickers becomes possible. The computed gain is transmitted as a gain signal to a one-field delay unit 109, and is inputted into the gain control unit 102 after passage of one field scanning time. In the gain control unit 102, a level of a brightness signal inputted from the image pick-up element 101 according to a gain signal, and then the processing described above is repeated.
A timing chart for the processing above is shown in FIG. 9. In FIG. 9, each of the brightness signals from start to end of scanning for the n-th field is added in the integrator 107 for obtaining an integrated value for the n-th field. Then each of brightness signals from start to end of scanning for the n+1-th field is also added in the integrator 107 to obtain an integrated value for the n+1-th field. In this step, the integrated value for the n+1-th field is inputted into the gain computing unit 108 at the same timing to obtain a gain for the n-th field.
Further, each of brightness signals from start to end of scanning for the n+2-th field is added in the integrator 107 to obtain an integrated value for the n+2-th field. At the same timing, transmission of a gain for the n-th field to the next block is held, namely delayed by one-field scanning time, and at the same time an integrated value for the n+1-th field is inputted into the gain computing unit 108 to obtain a gain for the n+1-th field.
Further each of brightness signals from start to end of scanning for the n+3-th field is added in the integrator 107 to obtain an integrated value for the n+2-th field. In this step, at the same timing, a gain for the n-th field to the next block is held, namely delayed by one-field scanning time, and at the same time an integrated value for the n+1-th field is inputted into the gain computing unit 108 to obtain a gain for the n+1-th field.
The processing at the timing above is, in FIG. 8, achieved by receiving a synch. signal generated by a synch. signal generator 110 with the integrator 107, gain computing unit 108, and one-field delay unit 109. For this reason, gain control with flickers having been corrected, is executed to a brightness signal outputted from the gain control unit 102 always according to a brightness signal for a field ahead by three fields from a current one, and image display is executed according to signals having been subjected to gain control.
Also in the digital type of solid image pick-up device based on the conventional technology, to suppress the flickers in a fluorescent lamp as described above, there is a method of suppressing a time for fetching a reflected light from an object, namely a time for receiving light at one pixel to {fraction (1/100)} sec. In this case, for the time of {fraction (1/100)} sec which is equivalent to a discharge interval in a fluorescent lamp twinkling at a frequency of 100 Hz, each pixel in a CCD can obtain a signal indicating a quantity of light including flickers, and an excessive signal including flicker becomes not so remarkable.
Further in the digital type of solid image pick-up device based on the conventional technology, it is possible to suppress generation of periodical flickers by providing a mechanical iris capable of changing a time for receiving light once for a pixel.
However, the image pick-up device capable of suppressing flickers in a fluorescent lamp used in an analog type of image pick-up tube based on the conventional technology is an image pick-up device capable of suppressing fluorescent lamp flickers to an analog type of image pick-up image equipped with an A/D converter and a D/A converter, and configuration of the device is relatively large, and can not be used for a compact and digital type of a solid image pick-up device using a CCD or the like.
A compact type of CCD camera is often used as a television camera used in a television conference system or in a television telephone system, and an image pick-up device capable of suppressing flickers in a fluorescent lamp in the analog type of image pick-up tube based on the conventional technology can not be used for the purposes as described above. In a case of a television telephone system using a personal computer, there is no way but to decrease the number of screens transmitted for a unit time because of a limit in a band width in an exchanger, which results in increase of a percentage of flickers included in one screen.
Also as gain control for a brightness signal for the n+3-th field is executed according to an integrated value for the n-th signal, there is no relation with a field to be scanned next, so that adjustment for continuous brightness between successive fields can not be achieved. Further, a brightness signal obtained through gain control has been subjected to the feedback processing relating to all the integrated values used in the processor for computing a gain, and when an unexpected noise from outside is mixed in the brightness signal, a brightness signal affected by the noise is successively generated, which is disadvantageous.
Also in the digital type of solid image pick-up device based on the conventional technology, in the method of fixing a time for receiving light once to {fraction (1/100)} sec to suppress flickers in a fluorescent lamp as described above, there has been the problem that the automatic iris function for obtaining optimal brightness by changing a time for receiving light according to luminous intensity of illumination therearound can not be used. In addition, if a mechanical iris is used, configuration of the device becomes complicated and large, which disadvantageously results in cost increase.
It is an object of the present invention to provide an image processing apparatus and an image processing method capable of suppressing flickers in a fluorescent lamp and applicable in a digital type as well as an analog type of television cameras, and to a computer-readable recording medium with a program for making a computer execute the method stored therein.
With the present invention, to make a brightness signal generated by flickers included in a field as a current object for image processing not so remarkable, a pixel average value for one field in image data in the field and a pixel average value for a plurality of fields in present and past image data for the number of fields equivalent to an interference cycle between an image pick-up frequency of the image pick-up unit and a twinkling frequency of illumination are computed by a first unit, and computing using the pixel average value for one field and that for a plurality of fields computed as described above respectively is executed by a second unit to each of image data in the field as a current object for image processing to generate corrected image data, so that it is possible to suppress flickers by taking into account not only flickers included in a field as a current object for image processing but also flickers included in a plurality of fields continuously scanned in the past.
With the present invention, in addition to the actions described above, corrected image data can be generated through simple computing consisting of a step of division and a step of multiplication, so that computing for image processing can be made at a higher speed.
With the present invention, to make a brightness signal generated by flickers included in a field as a current object for image processing not so remarkable, a pixel integrated value for one field in image data in the field and a pixel integrated value for a plurality of fields in present and past image data for the number of fields equivalent to an interference cycle between an image pick-up frequency of the image pick-up unit and a twinkling frequency of illumination are computed by a first unit, and computing using the pixel integrated value for one field and that for a plurality of fields computed as described above respectively is executed by a second unit to each of image data in the field as a current object for image processing to generate corrected image data, so that it is possible to suppress flickers by taking into account not only flickers included in a field as a current object for image processing but also flickers included in a plurality of fields continuously scanned in the past.
With the present invention, in addition to the actions described above, the number of image data required for computing an integrated value can be decreased, which enables image processing at a higher speed.
With the present invention, to make a brightness signal generated due to flickers included in a field as a current object for image processing not so remarkable, a pixel average value for one field in image data in the field and a pixel average value for a plurality of fields in present and past image data for the number of fields equivalent to an interference cycle between an image pick-up frequency of the image pick-up device and a twinkling frequency of illumination are computed, and corrected image data is generated by executing the computing using the pixel average value for one field and that for a plurality of fields computed as described above respectively to image data in a field as a current object for image processing, so that it is possible to suppress flickers by taking into account not only flickers included in a field as a current object for image processing but also flickers included in a plurality of fields continuously scanned in the past.
With the present invention, to make a brightness signal generated due to flickers included in a field as a current object for image processing not so remarkable, a pixel integrated value for one field in image data in the field and a pixel integrated value for a plurality of fields in present and past image data for the number of fields equivalent to an interference cycle between an image pick-up frequency of the image pick-up device and a twinkling frequency of illumination are computed, and corrected image data is generated by executing the computing using the pixel integrated value for one field and that for a plurality of fields computed as described above respectively to image data in a field as a current object for image processing, so that it is possible to suppress flickers by taking into account not only flickers included in a field as a current object for image processing but also flickers included in a plurality of fields continuously scanned in the past.
With the present invention, in a computer program for a computer, to make a brightness signal generated due to flickers included in a field as a current object for image processing not so remarkable, a pixel average value for one field in image data in the field and a pixel average value for a plurality of fields in present and past image data for the number of fields equivalent to an interference cycle between an image pick-up frequency of the image pick-up device and a twinkling frequency of illumination are computed, and corrected image data is generated by executing the computing using the pixel average value for one field and that for a plurality of fields computed as described above respectively to image data in a field as a current object for image processing, so that it is possible to suppress flickers by taking into account not only flickers included in a field as a current object for image processing but also flickers included in a plurality of fields continuously scanned in the past.
With the present invention, in a computer program for a computer, to make a brightness signal generated due to flickers included in a field as a current object for image processing not so remarkable, a pixel integrated value for one field in image data in the field and a pixel integrated value for a plurality of fields in present and past image data for the number of fields equivalent to an interference cycle between an image pick-up frequency of the image pick-up device and a twinkling frequency of illumination are computed, and corrected image data is generated by executing the computing using the pixel integrated value for one field and that for a plurality of fields computed as described above respectively to image data in a field as a current object for image processing, so that it is possible to suppress flickers by taking into account not only flickers included in a field as a current object for image processing but also flickers included in a plurality of fields continuously scanned in the past.
With the present invention, to make a brightness signal generated due to flickers included in a field as a current object for image processing not so remarkable, a pixel average value for one field in image data in the field and a pixel average value for a plurality of fields in present and past image data for the number of fields equivalent to an interference cycle between an image pick-up frequency of the image pick-up device and a twinkling frequency of illumination are computed by an integrated value computing unit, and corrected image data is generated by executing the computing using the pixel average value for one field and that for a plurality of fields computed as described above respectively to image data in a field as a current object for image processing with a corrected image data generating unit, so that it is possible to suppress flickers by taking into account not only flickers included in a field as a current object for image processing but also flickers included in a plurality of fields continuously scanned in the past.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.